Force dissipating impactor device

ABSTRACT

A force dissipating impactor device is comprises a bar member including a hollow shaft, a first end, and a second end. The first end of the impactor device provides an impaction surface and the opposite second end of the impactor device provides an implant engagement surface. The implant engagement surface is contoured to mate with a surface of the implant member. The impaction surface is configured to be struck with a mallet or other tool. A plurality of holes are provided in the shaft and penetrate the surface of the bar member. The plurality of holes provided on the shaft surface of the bar member may be arranged such that a line passing axially along the shaft surface intersects at least one of the plurality of holes. Further, the plurality of holes may be arranged in a staggered matrix around the shaft surface.

FIELD

This application relates to the field of impacting devices, such asthose used to provide impact force to a prosthetic component in order tosecure the prosthetic component to another device or to tissue.

BACKGROUND

Many orthopaedic procedures involve the implantation of prostheticdevices to replace badly damaged or diseased bone tissue. Commonorthopaedic procedures that involve prosthetic devices include total orpartial hip, knee and shoulder replacement. For example, a hipreplacement often involves a prosthetic femoral implant. The femoralimplant usually includes a rigid stem that is secured within the naturalfemur bone tissue. The femoral implant further includes a rounded headthat is received by, and may pivot within, a natural or artificial hipsocket. Shoulder replacement is somewhat similar, and typically includesa humeral implant that includes a rigid stem and a rounded head. Therigid stem is secured within the natural humerus bone tissue and therounded head is pivotally received by a shoulder socket.

Increasingly, prosthetic devices are provided as subcomponents that areassembled during surgery. In particular, the different anatomies ofdifferent patients require that prosthetic devices such as femoral andhumeral implants be available in different sizes and configurations. Byway of simplified example, a humeral implant may be available in as manyas six or more humeral head diameters. Stems may similarly vary in sizeand/or in shape. Because of differences in patients and individualconditions, it is advantageous that the surgeon have at her disposalmany configurations and sizes of implants. Instead of providing aseparate implant for each possible combination of features, implants areprovided as modular kits of subcomponents that allow the surgeon to mixand match different subcomponents to achieve the most advantageouscombination for the patient. Thus, the surgeon can pick from severalsizes or configurations of each component and combine the components toform an implant having an optimal combination of features.

One example of a modular implant is the humeral implant 10 shown inFIGS. 1 and 2. The humeral implant 10 includes a humeral head 12 thatmay be assembled onto a humeral stem 14. The humeral stem 14 isconfigured to be implanted in the intramedullary tissue of a naturalhumeral bone, while the humeral head 12 is configured to be receivedinto the shoulder socket or glenoid cavity.

In the exemplary modular implant of FIGS. 1 and 2, an intermediatecomponent 16 is provided between the humeral head 12 and the humeralstem 14. The intermediate component 16 is a two part insert thatincludes a stem insert 17 and a head insert 19. The stem insert 17 isprovided within a cavity at the end of the stem 14. The head insert 19includes a truncated ball portion 21 and a frusto-conical portion 23.The truncated ball portion 21 of the head insert is configured to fitwithin a receptacle in the stem insert 17. The frustro-conical portion23 serves as a tapered plug 16 that is designed to be received by atapered receptable 28 in the humeral head 12. It can be appreciated thatthe surgeon may secure alternative humeral head 12 designs on the samehumeral stem 14, thus providing the surgeon with a broad array ofhumeral head size options.

Once the components are selected, such as the humeral head 12, thehumeral stem 14, and the intermediate component 16 of FIGS. 1 and 2, thecomponents are assembled. One popular method of securing implantcomponents together involves the use of a Morse taper. The components ofFIGS. 1 and 2 by way of example include a Morse taper arrangement. Inparticular, a Morse taper is a feature in which a tapered malecomponent, e.g., the tapered plug 23 of the head insert 19, is receivedinto a tapered female component, e.g., the receptacle 28 of the humeralhead 12. The taper angle of the plug 23 is preferably, but need not be,slightly less than the taper angle of the receptacle 28. In use, theplug 23 advances into the receptacle 28, as indicated by arrow 29, untilit begins to engage the receptacle 28. The further into the receptaclethe plug 23 is forced, the more tightly it engages the humeral head 12.

The force applied to secure the plug 23 within the receptacle 28 isproportional to the retention force of the plug 23 within the receptacle28. Thus, if a sufficient amount of force is applied, then the humeralhead 12 will be securely fastened to the humeral stem 14 via the insert16. Other prosthetic devices employ Morse tapers for substantially thesame reasons.

To apply sufficient force to lock the Morse taper arrangement betweenthe humeral head 12 and the plug 23, it is known to impact the humeralhead 12 such that the impact force directs the humeral head 12 towardthe plug 23 and humeral stem 14. The impact force drives the plug 23into the receptacle 18 and forms the Morse taper lock. A hammer ormallet is typically struck directly on the head, or through an impactordevice.

During assembly of the implant, the surgeon (or other person) may impactthe prosthetic implant several times without knowing if sufficient forcehas been applied to lock the Morse taper sufficiently. In order to besure that the Morse taper is locked, the surgeon or assistant may useexcessive force. The use of excess force is undesirable because of thepotential for damage to the bone tissue or the implant device. Forexample, the use of excess force may disengage the intermediatecomponents between the head 12 and the stem 14, such as the insertcomponents 17 and 19, from their locked position.

Thus, there is a need for assisting surgical personnel in applying theproper amount of force to a Morse taper to lock the Morse taper. Inparticular, it would be advantageous to provide an impactor devicecapable of dissipating the force that is transmitted through theimpactor and to an implant when locking a Morse taper. Such an impactorwould serve to limit the application of excessive force and anyassociated damage. The need for such a device is widespread as Morsetapers have commonly been used for connection of many types of implantdevices. It would also be advantageous if such an impactor could bemanufactured simply and at a low cost.

SUMMARY

A force dissipating impactor device is disclosed herein. The disclosedimpactor device is configured to reduce the forces transmitted throughthe impactor device to an implant. The impactor device comprises a barmember comprising a hollow shaft, a first end, and a second end. Thefirst end of the impactor device provides an impaction surface and theopposite second end of the impactor device provides an implantengagement surface. A plurality of holes are provided in the shaft andpenetrate the surface of the bar member.

In one embodiment, the plurality of holes provided on the shaft surfaceof the bar member are arranged such that a line passing axially alongthe shaft surface intersects at least one of the plurality of holes. Inthis embodiment, the plurality of holes may be arranged in a staggeredmatrix that is provided around the shaft surface. In one embodiment,each row of the staggered matrix comprises four holes, and each hole ina row is situated ninety degrees relative to an adjacent hole in therow.

The implant engagement surface on the first end of the impactor deviceis contoured to mate with a surface of the implant member. Thus, in oneembodiment, the implant engagement surface is rounded and concave andthe surface of the implant member is rounded and convex. In oneembodiment, the impactor device is between five and nine inches inlength, and is preferably about seven inches in length. This lengthallows the impactor device to be easily handled by the surgeon.

The above described features and advantages, as well as others, willbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and accompanyingdrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary prior art humeral implant;

FIG. 2 shows a diagram of the humeral head, humeral stem, and insert forthe humeral implant of FIG. 1;

FIG. 3 shows a perspective view of a force dissipating impactor device;

FIG. 4 shows a side view of the impactor device of FIG. 3;

FIG. 5 shows a perspective view of the impactor device of FIG. 3 from anend portion of the impactor device;

FIG. 6 shows a side view of an alternative embodiment of the impactordevice of FIG. 3;

FIG. 7 shows a cross-sectional view of the impactor device along lineVII-VII of FIG. 6;

FIG. 8 shows a cross-sectional view of the impactor device along lineVIII-VIII of FIG. 6;

FIG. 9 shows a cross-sectional view of the impactor device along lineIX-IX of FIG. 6; and

FIG. 10 shows an expanded polar coordinate view of the shaft portion ofthe impactor device of FIG. 3 with the holes arranged in a staggeredmatrix.

DESCRIPTION

With reference to FIGS. 3-5, an impactor device 50 is disclosed. Theimpactor device 50 is provided as an elongated bar member 52 thatincludes a shaft portion 54, a grip 55, a first end 56, and a second end58. The first end 56 provides an impaction surface and the second endprovides a force distributing surface in the form of an implantengagement surface. A plurality of holes 60 are formed in the shaftportion 54.

In the embodiment of FIGS. 3-5, the shaft portion 54 of the impactordevice 50 is generally cylindrical in shape. The shaft portion 54 ishollow with a channel 62 extending axially along the center of the shaftportion. The channel 62 is surrounded by an exterior wall 62. Althoughthe exterior wall 62 is cylindrical in the embodiment of FIGS. 3-5, oneof skill in the art will recognize that the exterior wall may be any ofnumerous other shapes, such as box-shaped.

A plurality of holes 60 extend through the exterior wall 62 of the shaftportion 54 and into the axial channel 62, resulting in a perforatedshaft portion 54. In the embodiment of FIGS. 3-5, the plurality of holes60 are arranged on the shaft portion 54 such that any given line passingaxially along the surface of the exterior wall will intersect at leastone of the plurality of holes 60. To obtain this result, the holes 60 onthe shaft portion 54 may be arranged in a staggered matrix around theshaft.

FIG. 10 shows an expanded polar coordinate view of the shaft portion 54further displaying the staggered matrix arrangement of the holes. Thisview shows the shaft portion 54 “unwrapped” along the central axis suchthat the leftmost position is a zero degree position and the right mostposition is a three hundred sixty degree position radially relative tothe central axis of the shaft. As shown in FIG. 10, the holes 60 arearranged in a staggered matrix such that the holes 60 in one row areoffset from the holes in an adjacent row. In the disclosed embodiment,seven rows of holes 60 are provided with four holes in each row. Theholes 60 overlap in the axial direction such that a line extendingaxially along the shaft portion, such as line 90, will intersect one ormore of the holes 60. With this arrangement, the holes in each row aresituated at ninety degree increments around the shaft, as can be seenfrom FIGS. 8 and 9. In other words, the center of a hole in a row isninety degrees removed from the center of an adjacent hole in the row.In the disclosed embodiment, the diameter of each hole is 0.379 inch.

With reference again to FIGS. 3-5, the grip 55 of the impactor device 50is provided next to the shaft portion 54, toward the first end 56 of theimpactor device 50. The grip 55 includes a plurality of fins 72 thatextend axially along a length of the shaft surface. The fins 72 areseparated by axial indentations 74. The fins 72 and indentations 74provide a knurled surface that provides an aid in gripping the impactiondevice 50.

The first end 56 of the bar member 52 provides the impaction surface andis configured to receive a blow from a mallet or other striking device.In the embodiment of FIGS. 3-5, it can be seen that the impactionsurface is generally flat. This flat surface helps prevent the surgeonor surgical assistant from hitting the impactor device off axis. FIGS.6-9 show a similar embodiment to that of FIGS. 3-5, and identicalreference numerals are used to identify the same parts. However, in theembodiment of FIGS. 6-9, the impaction surface on the first end 56 ofthe bar member is convex. In this embodiment, the force of striking toolused by the surgeon is generally concentrated on a smaller area of theimpaction surface.

The second end 58 of the bar member is positioned opposite the firstend. The second end 58 of the bar member provides a force distributingsurface. The force distributing surface is configured to engage animplant member, and thus serves as an implant engagement surface. If theimplant member that will be contacted by the implant engagement surfaceis contoured, the implant engagement surface may be similarly contouredto mate with the surface of the implant member in a congruent fashion.The implant engagement surface shown in FIGS. 3-5 is designed to engagea convex rounded surface, such as the spherical humeral head of ahumeral implant. Thus, the implant engagement surface on the second end58 of the bar member 52 provides a concave rounded surface.

In one embodiment, the impactor device 50 is designed to be somewherebetween five and nine inches in length. This length generallyfacilitates ease of handling by the surgeon along with a sufficient sizefor many human implant devices. In one embodiment for use with a humeralimplant, the impactor device 50 is about seven inches in length. Ofcourse, one of skill in the art will recognize that the impactor deviceis not limited to a particular length and the impactor device may bedesigned to any number of different lengths.

The impactor device 50 may be comprised of any of several differentmaterials. Preferably, the material will be moldable, offer highflexural fatigue strength, rigidity, low wear, toughness and resistanceto repeated impact. In one embodiment, the impactor device 50 iscomprised of an acetal copolymer such as Celcon®. The simplicity of theimpactor device design and use of appropriate material will also allowthe impactor device to be easily cleaned through autoclaving.

The impactor device 50 is used by a surgeon or other surgical personnelto assemble a prosthetic device to be implanted in a patient. To thisend, the surgeon first chooses an appropriate design and size for thevarious components of the implant device based on the size and needs ofthe patient. The implant device comprises a first implant component anda second implant component to be connected by a Morse taper or similararrangement where the implant components are configured for connectionby forcing connection features on the first component into engagementwith connection features on the second component.

After selecting appropriate implant components, the surgeon selects animpactor device as set forth above. The impactor device includes a shaftportion, a grip portion, a first end with an impact surface and a secondend with an implant engagement surface. A plurality of holes are formedin the axial wall of the shaft portion. The implant engagement surfaceof the impactor device is configured to engage a surface of the firstimplant component in a congruent fashion.

The surgeon aligns the connection features of the first implantcomponent with the connection features of the second an implantcomponent. Next, the surgeon holds the impactor device by the gripportion 55 and brings the implant engagement surface 58 into contactwith the first implant component (e.g., the head 12 of the humeralimplant of FIGS. 1 and 2). The axis of the impactor device is orientedon the first implant component such that a force transmitted through theimpactor device will force the first implant component into fullengagement with the second implant component. After properly aligningthe impactor device, the surgeon strikes the impaction surface 56 on theimpactor device, thus transmitting a force through the impaction deviceand to the first implant component (e.g., the plug 19 into engagementwith the recess 28 in FIG. 2). This force is intended to bring theconnection features on the first implant component into engagement withthe connection features on the second implant component. The surgeon maybe required to strike the impaction surface 56 one or more times tobring the connection features on the first implant component into fullengagement with the connection features on the second implant component.

When the surgeon strikes the impactor device, the impactor devicedissipates the force transmitted through the bar member and to theimplant. In particular, the holes 60 in the impactor device 50 providevoids in the shaft portion 54 so that the shaft portion 54 can compressand expand to dissipate energy. Furthermore, the orientation of theholes 60 not only limits the amount of force that is transmitted downthe shaft portion, but also helps to maintain the integrity of theimpactor device, such that the impactor device does not fracture,degrade or otherwise fail when struck with a mallet or other strikingdevice.

The staggered matrix orientation and size of the holes on the shaftportion can effectively dissipate about forty percent of the impactionforce imparted by a striking device. Thus, even if a five thousand poundforce is delivered by a mallet strike, the impactor device 50 willreduce that force to around three thousand pounds, which would be morethan enough force to cause the humeral head to engage the humeral insertfor most implants. At the same time, the reduced force is much lesslikely to result in disengagement of or damage to the intermediatecomponents in the implant device.

Although the present invention has been described with respect tocertain preferred embodiments, it will be appreciated by those of skillin the art that other implementations and adaptations are possible. Forexample, the impactor may take the form of different shapes than thoseshown in the figures, may include different features, may be differentlysized, or may be comprised of different materials than those disclosedherein. Moreover, there are advantages to individual advancementsdescribed herein that may be obtained without incorporating otheraspects described above. Therefore, the spirit and scope of the appendedclaims should not be limited to the description of the preferredembodiments contained herein.

1. An impactor device configured to impact an implant member, theimpactor device comprising: a bar member including a shaft surface, afirst end, and a second end, the first end including an impactionsurface and the second end including an implant engagement surface; anda plurality of holes provided in the shaft surface of the bar member. 2.The impactor device of claim 1 wherein the shaft surface of the barmember is cylindrical in shape.
 3. The impactor device of claim 1wherein the bar member is hollow.
 4. The impactor device of claim 1wherein the implant engagement surface is contoured to mate with asurface of the implant member.
 5. The impactor device of claim 4 whereinthe implant engagement surface is rounded and concave and the surface ofthe implant member is rounded and convex.
 6. The impactor device ofclaim 1 wherein the bar member is between five and nine inches inlength.
 7. The impactor device of claim 6 wherein the bar member isabout seven inches in length.
 8. The impactor device of claim 1 whereinthe plurality of holes are arranged on the shaft surface of the barmember such that any line passing axially along the shaft surfaceintersects at least one of the plurality of holes.
 9. The impactordevice of claim 1 wherein the plurality of holes are staggered on theshaft surface of the bar member.
 10. The impactor device of claim 9wherein the plurality of holes are arranged in a staggered matrix aroundthe shaft surface.
 11. The impactor device of claim 1 wherein theplurality of holes are arranged in a plurality of rows around the shaftsurface of the bar member.
 12. The impactor device of claim 11 whereineach row of the plurality of rows comprises four holes, and wherein witheach hole in each row is situated ninety degrees relative to an adjacenthole in the row.
 13. The impactor device of claim 1 wherein the barmember comprises an exterior wall and the shaft surface is provided onthe exterior wall.
 14. An impactor device configured to deliver animpact force, the impactor device comprising: a hollow perforated shaft;an impaction surface located on one end of the perforated shaft; and aforce distributing surface on the opposite end of the perforated shaft.15. The impactor device of claim 14 wherein the perforated shaftincludes a plurality of holes arranged in a pattern upon the shaft. 16.The impactor device of claim 15 wherein the plurality of holes arearranged in a staggered matrix upon the shaft.
 17. The impactor deviceof claim 15 wherein the pattern of the plurality of holes is such thatall lines extending axially along a surface of the shaft will contact atleast one of the plurality of holes.
 18. The impactor device of claim 14wherein the force distributing surface comprises an implant engagementsurface which is contoured to mate with a component of an implant.
 19. Amethod of assembling an implant, the method comprising the steps of: a)providing a first implant component and a second implant component, thefirst implant component and second implant component configured forconnection by forcing connection features on the first component intoengagement with connection features on the second component; b)providing an impactor device comprising a shaft including an axial wall,and impaction surface, and an implant engagement surface, wherein aplurality of holes are formed in the axial wall of the shaft; c)aligning the connection features of the first implant component with theconnection features of the second an implant component; d) contactingthe implant engagement surface of the impactor device with the firstimplant component; and e) striking the impaction surface of the impactordevice in order to deliver a force through the impactor device to thefirst implant component which brings the connection features on thefirst implant component into engagement with the connection features onthe second implant component.
 20. The method of claim 19 wherein thefirst implant component comprises a convex surface, and wherein theimplant engagement surface of the impactor device is concave andconfigured to engage the convex surface in a congruent fashion.